Refractory-metal tube.



W. D. COOLIDGE.

REFRACTORY METAL TUBE.

APPLICATION FILED FEB.20, I9I5.

Patented' May 15, 1917.

Inventor: WiHaTI D. Coolidge,

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Vjwesss: 0n IZ STATES PATENT OFFICE.,

WILLIAM D.

COOLIDGE, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, CORPORATION OF NEW YORK. Y

REFRACTORY-METAL TUBE.-

To all 'whom z't may concern:

Be it known that I, WILLIAM D. CooLIDGE, a citizen of the United States, residing at Schenectady, in the county of Schenectady,

State of New York, have invented certain new and useful Improvements in RefractoryMetal Tubes, of which the following is a specification.

My present invention relates to a method of preparing tubes from refractory metals,

lsuch as. tungsten or molybdenum.

The object of my invention is to provide for the construction of tubes of this nature which will be of uniform and homogeneous structure throughout. A more specific object of my invention is to prepare tubes of refractory material which will be suitable for use in electric furnaces of the resistance tube type such as are shown and described in U. s. Patents #1,004,557 and #1,006,620.

In preparing tubes of such metals it has heretofore been customary to miX powdered m'aterial with a plastic binding material, shape the mixture into tubes, subsequently remove the binding material and sinter the residue into a dense homogeneous body.

These various steps have been necessary because of the diliiculty of compacting the dry powder into auniform tubular massof suiiicient strength to be handled and which when sintered would be perfectly homogeneous and uniform in thickness. By using my improved apparatus and carrying out my process, however, I ain able to overcome the previous difliculties and produce tubes of uniform characteristics directly from the powdered material without the use of any binding material.

In carrying my invention into effect I provide a mold' of tubular form in which the-powder may be placed loosely. This mold is so constructed that a uniform heavy pressure may be appliedinternally in a .radial direction to ,the entire mass whereby it may be compressed against the outer wall of the mold. This outer'wall of the mold may then Abe utilized as a support for thetubular mass until it has been partially sintered and is strong enough to be handled.

My invention with further objects and advantages will best be understood b reference to the following description ta :en connection with the accompanying drawing in which Figure 1 illustrates one embodiment ofthe apparatus which may be emspecmcano of 'Letters Patent.

Patented May' 15, 1917.

Application led February 20, 1915. Serial No.' 9,582.

ployed in carrying my invention into effect, and Fig. 2 shows a finished tube adapted for use as a heating element for electric furnaces.

As shown in Fig. 1 my mold comprises an outer wall 1 of tubular form which may consist" of a tube of porcelain or other refractory material of the desired length. The

inner wall12 should be of flexible material and may' consist of a length of rubber tubing. A perforated metal tube 3 may be placed inside the rubber tubing in order to it may be placed in .the metallic casing 8 which is -filled with a liquid Aand the removable end 9 of the casing secured by means of the screw cap 10.V Hydraulic pressure may then be applied to the liquid in the casing in any convenient Way through the opening 11 in the removable end 9. The Ipressure thus applied acts upon the inner wall 2 'of the mold through the perforations in the pipe 3 and is distributed uniformly in a radial direction over the entire-area of this inner wall. As a result the powder in the space 5 is compressed in a uniform layer against the-outer wall 1 of the mold.

. After sufficient lpressure has been applied to compress the powdered mass to the desired degree the mold may be taken from the casing 8 and the end pieces 4 andthe inner wall 2 removed. The inner wall having been expanded by the pressure applied and being elastic will contract as s'oon as the pressure has been removed and shrink away from the compressed mass of powder. 'The outer wall 1 with the compressed mass adhering thereto may then be placed in a suitable furnace and heated to a temperature suliicient to partially sinter together the par-V ticles of which it is composed. This sintering operation will cause the mass to contract and separate from the wall 1 and will also give the tube sufficient strength so that it 'can be handled without breaking. The par tially sintered tube may then be placed` in a hydrogen atmosphere and current passed through it to heat-it to a temperature sufficiently high to complete the smtering operation. The resulting tube will be of uniform thickness and have a densel homogeneous structure. To adapt such tubes for use vin a furnace it is usually desirable tovprovide lthem with suitable terminals such as those indicated in Fig. 2. Difficulty has been experienced heretofore in the construction of heating .elements of tungsten in securing a satisfactory electrical contact between the tungsten and the supply conductors. I have completely overcome this difficulty, however, by casting a copper terminal around the end of the tube in a suitablemold. The

. casting operation should be carried on in a vacuum furnace to prevent oxidation of the tungsten. I also find it desirable to use copper which has been treated previous to casting with an oxidizable boronv material such as elemental boron, boron suboxid, or boron carbid, as described in Weintraub Patent #1,023,604. In this Way I secure a terminal which has a high electrical conductivity and which is autogenously joined to the metal of the tube.

vthe powder used may be either pure tungsten prepared Ias 4described 1n my prior Patent #1,082,933, or tungsten powder prepared with certain additions as described in that patent. -The process may also be employed in making tubes of lmolybdenum or other refractory metals, and if desired powdered refractory materials, such, for example, as thorium oxid may be mixed with the metal powder to vary the characteristics of the finished product.

What I claim as new and desire to secure by Letters Patent of the United States, is

The method of preparing tubular bodies of refractory metal which comprises filling' a tubular mold with powdered metal, compressing the mass of powder by a uniform pressure in a radial direction applied to the inner wall of the mold and heating the mass thus compacted to partially sinter it before detaching from the outer wall of the mold. In Witness whereof, I have hereunto set my hand this 17th day of February, 1915.

y IVILLIAM D. COOLIDGE. Witnesses:

H. C. BU'TCH, BENJAMIN B. HULL. 

